The present application claims priority to Japanese Application No. P10-295778 filed Oct. 16, 1998 which application is incorporated herein by reference to the extent permitted by law.
1. Field of the Invention
The present invention relates to a solid electrolyte battery incorporating a solid electrolyte or a gel electrolyte.
2. Description of the Related Art
In recent years, the performance of electronic apparatuses represented by video cameras and portable telephones has significantly been improved and the sizes of the same have considerably been reduced. Also size reduction and improvement in the performance of secondary batteries serving as power sources for the electronic apparatuses have been required. Hitherto, lead batteries and nickel-cadmium batteries have been employed as the secondary batteries. Moreover, research and development of new nonaqueous-electrolyte secondary batteries have energetically been performed each of which contains lithium or a lithium alloy as an active material of a negative electrode.
The nonaqueous-electrolyte secondary battery containing lithium or the lithium alloy as the active material of the negative electrode exhibits a high energy density. The foregoing nonaqueous-electrolyte secondary battery suffers from a problem in that the performance deteriorates owing to growth of dendrite and undesirable shortening of the lifetime against charge and discharge cycles. A nonaqueous-electrolyte secondary battery contains, as the active material of the negative electrode, a material, such as a substance, which is able to dope/dedope lithium ions. Moreover, the nonaqueous-electrolyte secondary battery contains, as the active material of the positive electrode, a composite lithium oxide, such as lithium-cobalt oxide or lithium-nickel oxide. The nonaqueous-electrolyte secondary battery having the above-mentioned structure is free from deposition and dissolution reactions of lithium when the reactions of the electrodes are performed. Therefore, the nonaqueous-electrolyte secondary battery exhibits excellent lifetime against charge/discharge cycles.
Recently, a so-called solid electrolyte battery has been suggested as the nonaqueous-electrolyte secondary battery which contains a carbon material or graphite to constitute the negative electrode. The solid electrolyte battery contains a solid electrolyte or a gel electrolyte. Among the solid electrolyte batteries, a solid electrolyte battery of a type containing a gel electrolyte obtained by plasticizing a polymer material with nonaqueous electrolyte solution exhibits high ion conductivity at room temperatures. Therefore, the above-mentioned secondary batteries have been expected as promising secondary batteries.
The foregoing solid electrolyte battery is free from apprehension of leakage of solution and a necessity for providing a sealing structure using an outer can which has been required for the conventional structure. Therefore, the battery can be manufactured by encapsulating a winding-type electrode consisting of a positive electrode and a negative electrode with a moistureproof laminated film. Therefore, the solid electrolyte battery permits reduction in the weight and thickness as compared with the conventional structure. As a result, the energy density of the battery can furthermore be improved.
The solid electrolyte battery of the foregoing type suffers from a problem in that the discharge load characteristics is inferior to those of the nonaqueous-electrolyte secondary battery because the ion conductivity of the gel electrolyte is half of the ion conductivity of the nonaquaous electrolyte.
To overcome the foregoing problems experienced with the conventional techniques, an object of the present invention is to provide a solid electrolyte battery which does not deteriorate discharge load characteristics thereof and which is able to raise the energy density.
To achieve the foregoing object, according to one aspect of the present invention, there is provided a solid electrolyte battery comprising: a wound electrode incorporating a positive electrode incorporating an elongated positive-electrode collector having two sides on which positive-electrode active material layers are formed, a negative electrode incorporating an elongated negative-electrode collector having two sides on which negative-electrode active material layers are formed and a solid electrolyte layer formed between the positive electrode and the negative electrode such that the positive electrode and the negative electrode are laminated and wound, wherein when an assumption is made that the total thickness of a pair of the positive-electrode active material layers formed on the two sides of the collector for the positive electrode is total film thickness A and the total thickness of a pair of the negative-electrode active material layers formed on the two sides of the collector for the negative electrode is total thickness B, the total film thickness A of the positive-electrode active material layers satisfies a range from 60 xcexcm to 150 xcexcm, and ratio A/B of the total film thickness A of the positive-electrode active material layers with respect to the total thickness B of the negative-electrode active material layers satisfies a range from 0.5 to 1.2.
Since the solid electrolyte battery according to the present invention is structured as described above, the energy density of the battery can be raised without deterioration in the discharge load characteristics of the battery when an optimum value of the thickness ratio A/B of the total film thickness A of the negative-electrode active material layers with respect to the total thickness B of the negative-electrode active material layers is obtained.
Other objects, features and advantages of the invention will be evident from the following detailed description of the preferred embodiments described in conjunction with the attached drawings.